New data are presented for the room temperature, static compression of iron to 78 GPa with solid neon and argon as pressure-transmitting media. X ray diffraction studies have been performed on a geophysically relevant material, for the first time to such pressures under quasihydrostatic conditions, in a diamond anvil cell. The hydrostatic technique leads to increased precision in the measurement of high pressures and has placed closer constraints on the equation of state of &egr; iron. From a linear least squares fit of a finite strain equation of state to the present data combined with earlier, low-pressure data for metastable &egr; iron, the preferred values for the zero-pressure isothermal bulk modulus, K0, and first pressure derivative, K'0, are 192.7 (¿9.0) GPa and 4.29 (¿0.36), respectively. The zero-pressure volume for the &egr; phase is 6.687 (¿0.018) cm3/mol. On the basis of the pressure-volume curve calculated from fits of the finite strain equation of state, &egr; iron appears to be less compressible under nonhydrostatic conditions, but the differences are within the error of the nonhydrostatic experiment. The results also confirm that the absence of a soft medium in static compression experiments with the diamond anvil cell results in an overestimate of the unit cell volume (measured with the incident X ray beam parallel to the load axis) for pressures calculated with the nonhydrostatic ruby calibration scale. It is found that for &egr; iron, substantial compensation for this nonhydrostatic effect is implicit in the nonhydrostatic ruby pressure scale up to intermediate strains. The hydrostatic data and the &egr; iron isotherm derived from shock wave experiments on iron samples are in very close agreement.